Lightweight and broadband 2D MoS2 nanosheets/3D carbon nanofibers hybrid aerogel for high-efficiency microwave absorption

Preparation of cellulose derived carbon/reduced graphene oxide composite aerogels for broadband and efficient microwave dissipation

The development of cellulose derived carbon-based composite aerogels with light weight, broad bandwidth and strong absorption remains a challenging task. In this work, the cellulose derived carbon/reduced graphene oxide composite aerogels were prepared by a two-stage process of chemical crosslinking and high-temperature carbonization. The results revealed that the as-fabricated binary composite aerogels had a unique lightweight characteristic and three-dimensional porous network structure, which was chemically crosslinked by epichlorohydrin. Furthermore, the weight concentration of graphene oxide (GO) had a notable influence on the electromagnetic parameters and microwave absorption properties of the composite aerogels. The obtained binary composite aerogel possessed the optimal microwave dissipation capability when the concentration of GO was 1.5 mg/mL. Remarkably, the minimum reflection loss reached -50.42 dB at a thickness of 2.47 mm and a filling ratio of 17.5 wt%. Concurrently, the composite aerogel with a comparable thickness of 2.73 mm showed a wide effective absorption bandwidth of 7.28 GHz, spanning the total Ku-band and extending into a portion of the X-band. The radar cross section contribution of binary composite aerogels in the far-field was also simulated by computer simulation technique. In addition, the potential microwave attenuation mechanism was proposed. It was believed that the results of this paper would offer a reference for the preparation of cellulose derived carbon-based composite aerogels as efficient and broadband microwave absorbers.

Aerogels based on Bacterial Nanocellulose and their Applications

Microbial cellulose stands out for its exceptional characteristics in the form of biofilms formed by highly interlocked fibrils, namely, bacterial nanocellulose (BNC). Concurrently, bio-based aerogels are finding uses in innovative materials owing to their lightweight, high surface area, physical, mechanical, and thermal properties. In particular, bio-based aerogels based on BNC offer significant opportunities as alternatives to synthetic or mineral counterparts. BNC aerogels are proposed for diverse applications, ranging from sensors to medical devices, as well as thermal and electroactive systems. Due to the fibrous nanostructure of BNC and the micro-porosity of BNC aerogels, these materials enable the creation of tailored and specialized designs. Herein, a comprehensive review of BNC-based aerogels, their attributes, hierarchical, and multiscale features are provided. Their potential across various disciplines is highlighted, emphasizing their biocompatibility and suitability for physical and chemical modification. BNC aerogels are shown as feasible options to advance material science and foster sustainable solutions through biotechnology.

MoS2 Lubricate-Toughened MXene/ANF Composites for Multifunctional Electromagnetic Interference Shielding

The design and fabrication of high toughness electromagnetic interference (EMI) shielding composite films with diminished reflection are an imperative task to solve electromagnetic pollution problem. Ternary MXene/ANF (aramid nanofibers)-MoS2 composite films with nacre-like layered structure here are fabricated after the introduction of MoS2 into binary MXene/ANF composite system. The introduction of MoS2 fulfills an impressive "kill three birds with one stone" improvement effect: lubrication toughening mechanical performance, reduction in secondary reflection pollution of electromagnetic wave, and improvement in the performance of photothermal conversion. After the introduction of MoS2 into binary MXene/ANF (mass ratio of 50:50), the strain to failure and tensile strength increase from 22.1 ± 1.7% and 105.7 ± 6.4 MPa and to 25.8 ± 0.7% and 167.3 ± 9.1 MPa, respectively. The toughness elevates from 13.0 ± 4.1 to 26.3 ± 0.8 MJ m-3 (~ 102.3%) simultaneously. And the reflection shielding effectiveness (SER) of MXene/ANF (mass ratio of 50:50) decreases ~ 10.8%. EMI shielding effectiveness (EMI SE) elevates to 41.0 dB (8.2-12.4 GHz); After the introduction of MoS2 into binary MXene/ANF (mass ratio of 60:40), the strain to failure increases from 18.3 ± 1.9% to 28.1 ± 0.7% (~ 53.5%), the SER decreases ~ 22.2%, and the corresponding EMI SE is 43.9 dB. The MoS2 also leads to a more efficient photothermal conversion performance (~ 45 to ~ 55 °C). Additionally, MXene/ANF-MoS2 composite films exhibit excellent electric heating performance, quick temperature elevation (15 s), excellent cycle stability (2, 2.5, and 3 V), and long-term stability (2520 s). Combining with excellent mechanical performance with high MXene content, electric heating performance, and photothermal conversion performance, EMI shielding ternary MXene/ANF-MoS2 composite films could be applied in many industrial areas. This work broadens how to achieve a balance between mechanical properties and versatility of composites in the case of high-function fillers.

Advanced integrated nanochannel membrane with oppositely-charged bacterial cellulose and functionalized polymer for efficient salinity gradient energy generation

Reverse electrodialysis (RED) systems employing charged nanochannels have gained prominence for harvesting salinity gradient energy. Nevertheless, fabricating nanochannel membranes with optimal ion selectivity and high energy conversion efficiency remains a significant challenge. In this study, we develop oppositely charged bacterial cellulose (BC)/polymer composite nano-channel membranes with precisely designed nanochannel architectures by integrating chemical modification with composite material technology. Initially, BC undergoes chemical modifications, including 2,2,6,6-Tetramethylpiperidine 1-oxy radical (TEMPO) oxidation and quaternisation. Subsequently, a polymer network is integrated into the modified BC network through a polymer synthesis technique. This approach successfully yields negatively charged BC/poly(sodium p-styrene sulfonate) (NBC/PSS) composite double-networked nanochannel membranes and positively charged BC/poly(dopamine) (PBC/PDA) composite double-networked nanochannel membranes. Notably, these membranes exhibit significantly enhanced ionic conductivities, with values of 0.0008 and 0.0014 S cm-1 for the NBC/PSS and PBC/PDA composites, respectively, while also demonstrating superior ion selectivity with cation transfer numbers of 0.9 and 0.1 respectively. Furthermore, a series connection of 30 BCE/charged polymer-based RED devices successfully powers an electronic calculator. This work offers novel insights into the design of BC-based RED devices by integrating chemical modification and polymeric composite strategies for efficient salinity gradient energy generation.

Bioinspired Hierarchical Composite for Multiband Defense

The optimization of electromagnetic microwave absorbing (EMA) materials for radar stealth has been a continuous endeavor. However, meeting the defense requirements across multiple-frequency bands in increasingly complex and variable environments remains challenging. Drawing inspiration from the cytoskeleton-organelle structure, we designed and prepared a hierarchical MXene/NiFe2O4/calcined melamine foam (MNC) composite. The composite exhibits efficient and adjustable microwave absorption, infrared stealth, and solar absorption performance through the synergistic interaction of the components and the spatial effect of its novel microstructure. The composite achieves a minimum reflection loss of -58.57 dB and an effective absorption bandwidth (EAB) of 7.00 GHz, both of which can vary with the thickness. MNC also offers stable infrared stealth performance for heat sources ranging from 37 to 300 °C and high solar absorptivity up to 96.2%, promoting ambient-temperature-adaptive infrared stealth through electricity-sunlight cooperative regulation. With exceptional environmental adaptability characteristics such as photothermal conversion, lightness, elasticity, and hydrophobicity, the MNC composite holds promise as a multispectrum defense material for radar, infrared, and visible light for various forms of equipment, clothing, and wearables in harsh conditions.

Synthesis strategies, regeneration, cost analysis, challenges and future prospects of bacterial cellulose-based aerogels for water treatment: A review

Clean water is an integral part of industries, agricultural activities and human life, but water contamination by toxic dyes, heavy metals, and oil spills is increasingly serious in the world. Aerogels with unique properties such as highly porous and extremely low density, tunable surface modification, excellent reusability, and thermal stability can contribute to addressing these issues. Thanks to high purity, biocompatibility and biodegradability, bacterial cellulose can be an ideal precursor source to produce aerogels. Here, we review the modification, regeneration, and applications of bacterial cellulose-based aerogels for water treatment. The modification of bacterial cellulose-based aerogels undergoes coating of hydrophobic agents, carbonization, and incorporation with other materials, e.g., ZIF-67, graphene oxide, nanoparticles, polyaniline. We emphasized features of modified aerogels on porosity, hydrophobicity, density, surface chemistry, and regeneration. Although major limits are relevant to the use of toxic coating agents, difficulty in bacterial culture, and production cost, the bacterial cellulose aerogels can obtain high performance for water treatment, particularly, catastrophic oil spills.

MoS2-based nanocomposites and aerogels for antibiotic pollutants removal from wastewater by photocatalytic degradation process: A review

Photocatalytic technologies based on molybdenum disulfide (MoS2) catalysts are effective, eco-friendly, and promising for antibiotic pollutants treatment. The technologies used by MoS2-based nanocomposites and aerogels for efficient degradation of antibiotics are reviewed in detail for the first time in this paper. The fundamental aspects of MoS2 were comprehensively scrutinized, encompassing crystal structure, optical properties, and photocatalytic principle. Then, the main synthesized methods and advantages/disadvantages for the preparation of MoS2-based nanocomposites and aerogels were systematically presented. Besides, a comprehensive overview of diverse MoS2-based nanocomposites and aerogels photo-degradation systems that enhanced the degradation of antibiotic pollutants were revealed. Meanwhile, the photo-degradation mechanism concentrated on the photoelectron transfer pathways and reactive oxygen species (ROS) were systematically evaluated. Finally, the challenges and perspectives for deeply development of MoS2-based nanocomposites and aerogels were discussed. This review may help researchers to deeply understand the research status of MoS2-based nanocomposites and aerogels for antibiotics removal, and makes clear the photo-degradation mechanism from photoelectron transfer pathways and ROS aspects of MoS2-based nanocomposites and aerogels.

Regulatable Phase Manipulation-Enhanced Polarization and Conductance Loss Enabling Hierarchical 3D Microsphere-like MoS2 with Efficient Microwave Absorption

Molybdenum disulfide (MoS2) has become a new type of microwave absorption (MA) material due to the abundant functional groups and defects, high polarization effect, and controllable structural design. However, the development of MoS2 has been limited by its inherently low conductance losses and imperfect impedance matching. This study employs ammonium ion (NH4+) intercalation as a phase manipulation strategy to enhance dielectric loss and form heterogeneous structures by incorporating highly conductive 1T phase into the 2H-MoS2 crystal phase. Additionally, the implementation of CTAB as a soft template agent for constructing layered three-dimensional microsphere structures improves impedance matching. The experimental findings demonstrate that the MA performance of MoS2 can be effectively regulated by controlling the 1T phase content and morphological structure design. It is worth noting that A-MoS2-2 possesses excellent multifrequency absorption capability. A-MoS2-2 has a minimum reflection loss (RL) of -53 dB at a coating thickness of 1.99 mm and an effective absorption bandwidth (EAB) of 5.6 GHz at a thinner coating thickness of 1.77 mm. This work improves the MA properties of MoS2 by introducing metallic phases and unique structural design, which opens up new ideas for the development of MA materials.

Combination strategy of large interlayer spacing and active basal planes for regulating the microwave absorption performance of MoS2/MWCNT composites at thin absorber level

Recently, molybdenum disulfide (MoS₂)/carbon has become a promising candidate for efficient microwave absorption. However, it is still challenging to simultaneously optimize the synergy of impedance matching and loss capability at the level of a thin absorber. Here, a new adjustment strategy is proposed by changing the concentration of precursor l-cysteine for MoS₂/multi-walled carbon nanotubes (MWCNT) composites to unlock the basal plane of MoS₂ and expand the interlayer spacing from 0.62 nm to 0.99 nm, leading to improved packing of MoS₂ nanosheets and more active sites. Therefore, the tailored MoS₂ nanosheets exhibit abundant sulfur-vacancies, lattice-oxygen, more metallic 1T-phase, and higher surface area. Such sulfur-vacancies and lattice-oxygen promote the electronic asymmetric distribution at the solid-air interface of MoS₂ crystals and induce stronger microwave attenuation through interface/dipole polarization, which is further verified by first-principles calculations. In addition, the expansion of the interlayer spacing induces more MoS₂ to deposit on the MWCNT surface and increases the roughness, improving the impedance matching and multiple scattering. Overall, the advantage of this adjustment method is that while optimizing impedance matching at the thin absorber level, composite still maintains a high attenuation capacity, which means enhancing the attenuation performance of MoS₂ itself offsets the weakening of the composite's attenuation ability caused by the decrease in the relative content of MWCNT components. Most importantly, adjusting impedance matching and attenuation ability can be easily implemented by separate control of l-cysteine content. As a result, the MoS₂/MWCNT composites achieve a minimum reflection loss value of -49.38 dB and an effective absorption bandwidth of 4.64 GHz at a thickness of only 1.7 mm. This work provides a new vision for the fabrication of thin MoS₂-carbon absorbers.

Sulfur vacancy regulation and multipolarization of NixCo1S nanowires-decorated biotemplated structures to promote microwave absorption

It is a novel and practical method to use natural porous biomaterials as microwave absorber. In this study, Ni_xCo₁S nanowires (NWs)@diatomite (De) composites with one-dimensional (1D)-NWs and three-dimensional(3D)-De composites were prepared by a two-step hydrothermal method using De as template. The effective absorption bandwidth (EAB) of the composite reaches 6.16 GHz at 1.6 mm and 7.04 GHz at 4.1 mm, covering the entire Ku band, and the minimum reflection loss (RLmin) is less than -30 dB. The excellent absorption performance is mainly due to the bulk charge modulation provided by the 1D NWs and the extended microwave transmission path within the absorber, coupled with the high dielectric loss and magnetic loss of the metal-NWS after vulcanization. We present a high-value method that combines vulcanized 1D materials with abundant De to achieve the lightweight broadband efficient microwave absorption at the first time.

Morphology and Microwave-Absorbing Performances of Rubber Blends with Multi-Walled Carbon Nanotubes and Molybdenum Disulfide

This study details microwave-absorbing materials made of natural rubber/nitrile butadiene rubber (NR/NBR) blends with multi-walled carbon nanotubes (MWCNTs) and molybdenum disulfide (MoS₂). The mechanical blending method and the influences of fabrication on the morphology and microwave-absorbing performance of resulting compounds were logically investigated. It was found that interfacial differences between the fillers and matrix promote the formation of MWCNTs and MoS₂ networks in NR/NBR blends, thus improving microwave-absorbing performance. Compared with direct compounding, masterbatch-based two-step blending is more conducive to forming interpenetrating networks of MWCNTs/MoS₂, endowing the resulting composite with better microwave attenuation capacity. Composites with MWCNTs in NR and MoS₂ in NBR demonstrate the best microwave-absorbing performance, with a minimum reflection loss of -44.54 dB and an effective absorption bandwidth of 3.60 GHz. Exploring the relationship between morphology and electromagnetic loss behavior denotes that such improvement results from the selective distribution of dual fillers, inducing networking and multi-component-derived interfacial polarization enhancement.

Enhanced osmotic energy conversion through bacterial cellulose based double-network hydrogel with 3D interconnected nanochannels

Hydrogel with 3D networks have shown great potential for ion transportation and energy conversion. However, the micron size pores of hydrogel greatly limit the ion selectivity and energy conversion performance. Here, we report a bacterial cellulose (BC) derived hydrogel membrane with double-network (DN) and tailored ion transport channels by rationally filling acrylic acid (AAc)-co-acrylamide (AAm)-co-methyl methacrylate (MMA) polymers into BC hydrogel micropores. Fabricated AAM/BC DN hydrogel membrane displays a unique hierarchical interconnected porous structure and 3D cation transport channels. From the results, the maximum power density reached up to 7.63 W·m^-2 at 50-fold salinity gradient under alkaline conditions (pH 11). Interestingly, the power density of 45.5 W·m^-2 was achieved through acid-base neutralization reaction. Furthermore, hydrogel successfully obtained a power density of 28.4 W·m^-2 from a mixed system of paper black liquor wastewater/seawater. The results of this investigation suggested the enormous potential of BC-based nanofluidic membrane in sustainable osmotic energy conversion.

Natural Hollow Fiber-Derived Carbon Microtube with Broadband Microwave Attenuation Capacity

Constructing hierarchical structures is indispensable to tuning the electromagnetic properties of carbon-based materials. Here, carbon microtubes with nanometer wall thickness and micrometer diameter were fabricated by a feasible approach with economical and sustainable kapok fiber. The carbonized kapok fiber (CKF) exhibits microscale pores from the inherent porous templates as well as pyrolysis-induced nanopores inside the wall, affording the hierarchical carbon microtube with excellent microwave absorbing performance over broad frequency. Particularly, CKF-650 exhibits an optimized reflection loss (RL) of −62.46 dB (10.32 GHz, 2.2 mm), while CKF-600 demonstrates an effective absorption bandwidth (RL < −10 dB) of 6.80 GHz (11.20−18.00 GHz, 2.8 mm). Moreover, more than 90% of the incident electromagnetic wave ranging from 2.88 GHz to 18.00 GHz can be dissipated by simply controlling the carbonization temperature of KF and/or the thickness of the carbon-microtube-based absorber. These encouraging findings provide a facile alternative route to fabricate microwave absorbers with broadband attenuation capacity by utilizing sustainable biomass.

1D CNT-Expanded 3D Carbon Foam/Si3N4 Sandwich Heterostructure: Utilizing the Polarization Compensation Effect for Keeping Stable Electromagnetic Absorption Performance at Elevated Temperature

Modern electromagnetic (EM) absorbing materials (EAMs) are experiencing a revolution triggered by advanced information technology. Simultaneously, the diverse harsh EM application scenarios entail a more stringent appeal of practicability to EAMs, especially under high-temperature conditions. Therefore, exploring EAMs with both excellent absorbing performance and practicability at elevated temperatures is necessary. Herein, a novel 3D porous carbon foam/carbon nanotubes@Si₃N₄ (CF/CNTs@Si₃N₄) heterostructure was constructed by the chemical vapor infiltration process. The optimally grown 1D CNTs embedded in 3D CF/Si₃N₄ are utilized to provide abundant nanointerface coupling effects to compensate for the excessive increase in the conductive loss during rising temperature to realize a self-adjustment in response to high temperature. A high-efficiency EM absorption over a wide temperature range from 25 to 480 °C was achieved (with a ≥90% absorbing ratio covering the whole X-band). In addition, the Si₃N₄ coating can improve the thermal stability of the carbon matrix and maintain the tailored inner structure. Multiple investigations into other environmental adaptabilities also exhibited the application perspective of such a heterostructure. This work points out a new strategy for preparing designable, efficient, and high-temperature applicable EAMs, promoting the diverse development of electronic devices.

Sustainable Kapok Fiber-Derived Carbon Microtube as Broadband Microwave Absorbing Material

The design of hierarchical structures from biomass has become one of the hottest subjects in the field of microwave absorption due to its low cost, vast availability and sustainability. A kapok-fiber-derived carbon microtube was prepared by facile carbonization, and the relation between the structure and properties of the carbonized kapok fiber (CKF) was systematically investigated. The hollow tubular structures afford the resulting CKF composites with excellent microwave-absorbing performance. The sample with a 30 wt.% loading of CKF in paraffin demonstrates the strongest microwave attenuation capacity, with a minimum reflection loss of −49.46 dB at 16.48 GHz and 2.3 mm, and an optimized effective absorption bandwidth of 7.12 GHz (10.64–17.76 GHz, 2.3 mm) that covers 34% of the X-band and 96% of the Ku-band. Further, more than 90% of the incident electromagnetic wave in the frequency from 4.48 GHz to 18.00 GHz can be attenuated via tuning the thickness of the CKF-based absorber. This study outlines a foundation for the development of lightweight and sustainable microwave absorbers with a high absorption capacity and broad effective absorption bandwidth.

State of the Art and Prospects in Metal-Organic Framework-Derived Microwave Absorption Materials

Microwave has been widely used in many fields, including communication, medical treatment and military industry; however, the corresponding generated radiations have been novel hazardous sources of pollution threating human's daily life. Therefore, designing high-performance microwave absorption materials (MAMs) has become an indispensable requirement. Recently, metal-organic frameworks (MOFs) have been considered as one of the most ideal precursor candidates of MAMs because of their tunable structure, high porosity and large specific surface area. Usually, MOF-derived MAMs exhibit excellent electrical conductivity, good magnetism and sufficient defects and interfaces, providing obvious merits in both impedance matching and microwave loss. In this review, the recent research progresses on MOF-derived MAMs were profoundly reviewed, including the categories of MOFs and MOF composites precursors, design principles, preparation methods and the relationship between mechanisms of microwave absorption and microstructures of MAMs. Finally, the current challenges and prospects for future opportunities of MOF-derived MAMs are also discussed.